The fastest predator on Earth?: star-nosed mole

Eimer’s organ: touch receptors - 120 milliseconds to identify and consume prey

The Big Picture: Perception to Behavior


  • Sensory processes begin with stimuli
    • stimuli are forms of energy
    • internal or external


  • Receptors alert nervous systems (most animals)
    • use action potentials (membrane voltage)
    • results in a ‘sensation’


  • After a stimulus is processed, a response may be generated

Sensory systems work through neural pathways

  • Neurons =
    • sensory, interneurons, and motor neurons
    • Fundamental unit of the brain and nervous system**


  • Neuron structure is all about form and function
    • Most organelles located in the cell body
    • Highly branched extensions, called dendrites, receive signals


  • Neurons have a single axon to transmit signals
    • transmit pulses of electrical current
    • terminals connect nerve cells

(1) Sensory Reception



  • Sensory pathways have four basic functions:
    • reception, transduction, transmission, perception


  • Sensory pathway starts with stimuli


  • (1) Sensory reception:
    • sensory cells are specialized neurons
    • located inside or on outside of body
    • detect specific types of stimuli

(2) Sensory Transduction: Converting signals


  • Transduction:


  • Stimulus receptors change flow of ions across nerve cell membranes
    • opens/closes ion membrane channels along axon
    • Cl-, Na+, K+


  • Membrane potential: gradient that forces ions to passively move in one direction
    • can be processed by central nervous system
    • at rest, inside of cell is more negative than outside
    • magnitude of change in ion flow = strength of stimulus

(3) Sensory Transmission: action potentials (nerve impulse)


  • Transmission:


  • Action potential:
    • caused by change in membrane potential
    • travels along axon and flows to other cells


  • Receptor generates action potentials that travel to central nervous system
    • large stimulus = more action potentials


  • Speed of action potential depends on species
    • length of axons varies
    • vertebrate axons are insulated

Action Potential further explained…

(4) Sensory Perception: Processing the stimulus



  • Perception:


  • How does the brain know the difference in stimuli?
    • action potentials are not different from each other


  • Action potentials reach brain/spinal cord via dedicated neural pathways
    • brain distinguishes stimuli on the path they arrive
    • 100 million neurons with 100 trillion connections = human brain
    • actions potentials sent back to target receptors via motor neurons

If a tree falls in the woods……

Animal sensory receptors: Mechanoreceptors



  • Response to touch, stretch, motion and sound
    • Receptors sense physical deformation


  • Ion channels linked to structures that end outside cell
    • hair or cilia
    • bending/stretching structure generates response


  • Touch receptors often embedded in tissue

Diversity of mechanoreceptors on mouse face


Animal sensory receptors: Chemoreceptors


  • (1) Transmit information about solute concentrations
    • detect change in blood solutes → stimulate thirst


  • (2) Respond to individual kinds of molecules
    • glucose, O2, CO2, amino acids, pheromones


  • Stimulus molecule binds to a chemoreceptor
    • silk worms detect pheromones from females several kilometers away


  • Chemoreceptor becomes more or less permeable to ions

Taste and smell rely on chemoreceptors

Taste and smell rely on chemoreceptors

Animal sensory receptors: Electromagnetic



  • Receptors that detect light, electricity and magnetism


  • Animals create & detect electromagnetic energy to hunt


  • Used by animal kingdom to migrate
    • proteins can sense Earth’s magnetic fields
    • insects, birds & mammals

Animal sensory receptors: Electromagnetic



  • Receptors that detect light, energy and magnetism
    • may also create & detect electromagnetic energy



  • Used widely by animals to sense prey
    • 16% of fish species use electroreceptors to detect bioelectric fields from prey

Animal sensory receptors: Thermoreceptors


  • Receptors detect heat and cold


  • Hot pepper science has really helped!!!
    • Receptors that respond to capsaicin also respond to high temperatures
    • taste ’hot”: activate same receptors as hot soup
    • opposite for ‘cold’ flavor


  • Mammals: thermoreceptors for specific temperatures
  • Venomous snakes: infrared receptors to detect ‘warm’ prey

Animal sensory receptors: Pain




  • Pain receptors (nocioreceptors) detect stimuli that reflect harmful conditions
    • damaged or inflamed tissues
    • gene mutations can cause chronic insensitivity to pain (C.I.P.) by making nocioreceptos non-functional


  • Respond to damaged/inflamed tissues
    • perceived as pain
    • trigger defenses (withdraw)